(a) Field of the Invention
The present invention relates to a method for preparing a positive electrode active material for a lithium secondary battery, a positive electrode active material for a lithium secondary battery, and a lithium secondary battery including the same.
(b) Description of the Related Art
Recently, with respect to the trend of miniaturization and lightweight of portable electronic devices, the batteries used as power for the devices need to be have high performance and high capacity.
Batteries generate electric power by using materials capable of having an electrochemical reaction at positive and negative electrodes. Of these batteries, a representative example is a lithium secondary battery in which electric energy is generated due to a change in a chemical potential when lithium ions are intercalated/deintercalated at positive and negative electrodes.
The lithium secondary battery is manufactured by using a material capable of reversibly intercalating/deintercalating lithium ions for positive electrode and negative electrode active materials and charging an organic electrolyte or a polymer electrolyte between a positive electrode and a negative electrode.
As for the positive electrode active material for the lithium secondary battery, a lithium composite compound is used, and examples thereof may include metal composite oxides such as LiCoO2, LiMn2O4, LiNiO2, and LiMnO2, which have been researched.
Of these positive electrode active materials, Mn-based positive electrode active materials, such as LiMn2O4 and LiMnO2, are attractive since they are easy to synthesize, are relatively cheap, have relatively excellent thermal stability at the time of overcharging as compared with the other active materials, and have less pollution on environment. However, these materials have a drawback in that the capacity is small.
LiCoO2 is a representative positive electrode active material that is currently commercialized on the market since it has favorable electrical conductivity and a high battery voltage of about 3.7 V as well as excellent cycle lifespan characteristics, stability, and discharge capacity. However, LiCoO2 is not priced competitively since it is expensive and thus accounts for 30% or more of the battery price.
LiNiO2 is difficult to synthesize even though it provides the highest charge capacity in the above-mentioned positive electrode active materials. Moreover, the high oxidation state of nickel is a causative factor of deteriorating battery and electrode lifespan characteristics. Moreover, the self discharge of nickel is severe and reversibility of nickel is deteriorated. Moreover, nickel insufficiently secures stability and thus is difficult to commercialize.
For the improvement in stability and capacity of the battery, JP 2011-216485 discloses a positive electrode active material for a lithium secondary battery, in which lithium nickel composite oxides having different particle size distributions and different compositions are mixed. Here, the degree of improvement is explained as a synergy effect due to the physical mixing of different positive electrode active materials.
KR2012-0017004 discloses a positive electrode active material for a lithium secondary battery, which is prepared by mixing precursors having different compositions and firing the mixture together with a lithium compound. However, since the firing temperature needs to be varied depending on the compositional ratio of Ni/Co/Mn in order to exhibit the maximum performance for the compositions, the corresponding technology is restricted to a mixture of precursors having very similar compositions.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.